1. Field of the Invention
This invention is useful in the field of double hung sash windows and is of particular use where it is desired to tilt a sash window for cleaning purposes or to remove the window to replace a broken pane of glass.
2. Description of the Prior Art
The pivoted or tilt-out double hung sash window is not a new concept but has been in use for many years. Its convenience for washing the outside of the window or for replacing a broken pane of glass in high-rise buildings has made such a window structure popular. The counterbalance system for holding the sash window in its open or closed position has progressed from a lead or iron counterweight to a balance spring assembly. The balance spring mechanism is enclosed in the side jamb liners or weather strips on each side of the window sash.
One of the problems which is present in the pivoted or tilt out sash window has been the retention of the end of the counterbalance spring which is attached to or removably secured to the window itself. Since the window is removable, its full weight will not be available to offset the pull of the counterbalance spring. When the window is removed, the connection between the window sash and the counterbalance spring is disconnected and unless a positive locking arrangement is effected, there will be no force to counteract with the counterbalance spring. The counterbalance spring will snap upwardly and may, after a few such releases, be deformed so that its effectiveness may be reduced.
There are many types of locking mechanisms which are available to overcome the problems outlined above. Reference may be had to U.S. Pat. Nos. 3,055,063; 3,108,335; 3,118,190; 3,124,849; 3,183,559; 3,184,784; 3,335,523; 3,462,882; and 3,482,354. In general these patents show a locking mechanism in which a block which is connected to the window sash by a disconnectable pin or bar rides in a vertical channel. The block has an auxiliary mechanism for locking the block upon tilting of the window. In some cases a frictional engagement is made by means of a cam which has an offset center and its outer edge engages a portion of the sidewalls of the channel. In other cases the frictional engagement is made by a transverse movement of a cam which again locks the block against a portion of the cam.
A still further type of locking mechanism comprises a hook which has a sharp point to engage a wall in the side jamb liner or weather strip. However, this type of locking engagement is subject to being dislodged and the counterweight spring may be released.
For the sake of economy, rigid plastic extrusions are used as side jamb liners or weather strips which guide the window sashes in their up and down movement. However, it has been found that the rigid plastic extrusions in past configurations often do not have enough strength to act as locking elements when the window sash is to be rotated 90.degree. from its normal position. To provide for sufficient strength for this purpose, the extruded elements would have to be made much thicker and would be more expensive.